I love many parts of Sihanoukville, yet hate just as many. Having gone there for the last three years, I have seen the rapid deterioration of the charming areas as well as the expansion of casinos, large hotels and sex tourism. It is the only place I have been that Viagra and condoms are sold on the counter of every shop like gum or breath mints are here. I think that says a lot. (I am glad about the availability of condoms however the price would be prohibitive to most Khmers. This is a service to protect tourists rather than the locals).
There are still beautiful beaches, fantastic little French breakfasts, delicious seafood dinners on the beach for $3 - $3.50, magnificent islands, welcoming Khmers, charming budget bungalows on the beach, a great night life and many more reasons to visit Sihanoukville.
Island trips are offered everywhere at various prices. If you are looking for a day trip, I would recommend the triple story boat by Suntours that goes to the outer islands rather than the cheap and easy Bamboo Island options. The boat is great, food very good, the equipment well maintained and good quality, the owner cares about the environment and the islands are divine. For an extra $10 you get a lot more. This is my theory on Cambodia, the cheapest options are cheap yet the more expensive options are still cheap and a far greater bargain. For $15 you can sit in a little wooden motorboat and get ferried from inner island to island with a beach BBQ and guaranteed no environmental thought for their impact; for $25 you can choose the Suntours boat, visit the far more beautiful outer islands in high comfort, go on guided walks up rivers and into the rain forest, snorkel on the reef in privacy (not with 3 other boats and a boose cruise in the water with you), fish (but you will have to throw them back if they are undersized - thank goodness), drink cocktails on the sun deck or at the bar, eat fresh shrimp, curries, rice dishes and salads, jump from the roof and enjoy the many other features I have forgotten. This is the real bargain as far as I am concerned.
Serendipity Beach has a long stretch of restaurants and bars. This area is safe at night and child friendly. We choose to eat at Moon Shack as it is owned by a Khmer family. The staff are all related and the kids running around at the back are the children of various staff members. There BBQ is the best. Don't worry about food poisoning if you order the BBQ; the seafood is fresh and delicious, hence Moon Shack has a loyal and regular clientele.
Serendipity Beach was the home of the backpacker and budget traveler. This year there seemed to be a much larger number of very dodgy looking older men. This concerns me. The sleaze of Cambodia loves the Victory Beach area and used to stay there. I am not sure why they are moving down to other beaches but I wish they would not. It would be a shame if the young party crowd were given further reasons to stay in Thailand rather than experiencing the magic Cambodia has to offer. (The primary reason the party crowd may move away is the police were closing down the beach bars at midnight. This is not good for business or Cambodia as a whole in my opinion).
There are other beaches that are quieter if that is what you are looking for. Beautiful as they are during daylight, I would not recommend traveling to remote beaches at night without good local knowledge about holdups and the like.
Do visit the waterfall on a Sunday with the locals - it is a hoot.
Check out the Pagoda on top of the hill.
Eat breakfast at the little French bakery on the hill up from Serendipity. He bakes his own croissants and breads, is really cheap and very French. If he is in a bad mood it can be entertaining.
"Sure" does not mean yes. "Sure" means if you want to believe this is the truth then it can be.
One other point - do not give in to the Tuk Tuk mafia. A ride from the beach to town or Victory to Serendipity is all the same - $2. If you agree to pay more you are ruining it for everyone else. $2 is already the tourist price. $3 is a joke and any more should be a crime.